Continental rifts are long, narrow fracture zones bound by faults along which continents eventually break apart in the plate tectonic process. The leading example on the modern Earth is the East African Rift, which stretches more than 3200 km from Djibouti through Ethiopia, Kenya, Uganda and Tanzania to Malawi. Continental rifts are well-known for their abundance of volcanoes, with Tanzania’s Kilimanjaro and Congo’s Nyiragongo providing well-known East African examples. The latter erupted in 2002, when its lava lake escaped through a flank in the volcano, devastating the town of Goma.
The volcanoes of the East African Rift also provide a long-standing riddle for geologists. Many of them produce rocks that are rich in carbonate, or require carbonate during the melting process in order to form; rare volcanoes such as Oldoinyo Lengai in northern Tanzania even erupt pure carbonate lava flows. The riddle has always been to explain where all this carbonate comes from. Why do rifts contain such concentrations of carbonate-bearing volcanic rocks when other tectonic environments do not?
Rifts are also the sites of massive CO2 degassing along faults and at volcanoes – much higher than in other areas around the world. Research is showing that the solution to the riddle lies in appreciating the depth of geological time, and in understanding the mobility of carbon as...
